Process for recovering gasoline from gas



May 19, 1931. F. A. HOWARD ET AL PROCESS FOR ARECOVERINGr GSOLINE FROM GAS o, (-451- if icieli Filed Feb. 20, 1926 fi C' (l` .FRANK /XHOWARD A AI SOO boob v hv@ QUNNK Patented May 19, 1931 UNITED STATES PArEN'n OFFICE FRANK A; HOWARD, OF ELIZBETH,'AND NATHANIEL E. LOOMIS, OF WESTFIELD, NEW JERSEY, ASSIGNORS TO STANDARD OIL DEVELOPMENT COMPANY, A. CORPORATIONl F DELAWARE PROCESS FOR RECOVERNG GASOLINE FROM lGAS application led February 20, 1926. Serial No. 89,644.

ThisA invention relatesv'to improvements in the art of recoverlng condenslble constltuents from hydrocarbon gases. -The invention will be fully understood from the following description, taken in connection with the accompanying drawing, in which the figure is a diagrammatic side elevation of a suitable 'form of apparatus. v

. Referring to the drawing, reference numeral 1 denotes an absorption or scrubbing tower, into which the gas to be treated is introduced through a pipe 2. This gas may be natural gas, still gases, or other suitable source of gasoline hydrocarbon vapors. When natural gas is used, it will ordinarily be compressed and cooled as a preliminary to the absorption. The condensate obtained in the compression and cooling operation may be introduced into tower 1 throughv pipe 3, or into some other suitable portion of the system, when desired. Fixed gases are taken oi from the absorption tower 1 through pipe 4, and an absorption liquid is introduced through pipe 5. The absorption stock (absorption liquid containing gasoline constituents and lighter hydrocarbons) is withdrawnrthrough ipe 6, through heat exchange means su sequently described, and then is7forwarded by pump 6 to a rectifying tower v constituents of the gas and substantiall non-volatile under the conditions impose Mineral seal oil, gas oil, heavy naphtha, or similar hydrocarbons, are suitable.

T e towers 7, 8, and 9 are each provided with liquid and vapor Contact means, for example bell-cap plates 10, preferably substantially. throughout the tower. Each tower has also a coolin or refrigerating coil 11 "i near its top and a eating coil 12, or other heating means, near its bottom. Outlet pipes v13, 14, and 15 are respectively connected to the towers 7, 8, and 9 adjacent their tops, valves 13', 14', and 15 being arranged in these pipes for regulating the pressure in the towers. The lrectification may be conducted in the presence of reflux formed only by the condensing action of the coils 11, or4 additional cool absorption oil may -be introduced through pipes 16, 17, and .18. The added oil may be of the same kind as that used in the absorption tower 1, or any other suitable oil.

The following is illustrative of the operation of our method, as applied to a gas having the following approximate composition:

Per cent Nitrogen and methane `54.8 Ethane 20.4 Carbon dioxide 0.2 Propane 14.7 Butane 6.9 Pentane and higher hydrocarbons 3.0

lit will be understood that the temperatures and pressures desirable will vary materially with the composition of the gases being treated, as well as with the nature and amount of the absorption liquid. The specific data given, therefore, are to be considered as i illustrative only. In accordance with our lnventlon, a plu,-

Fixed ases are substantially completely removed romthe absor tion stock in tower 7. The absorption stoc containing butane and hea-vier gasoline constituents, as well as some of thepropane, is withdrawn from pipe 19, inl whichl a valve 20 is arranged, to the intermediate portion of the tower 8. 'In that tower mostof the butane and anyresidual li hter hydrocarbons are separated by rectication. The absorption stock, which now contains-gasoline constituents substantially free from wild components, is passed through pi 21 to the tower 9. A valve 22 is arrange in the pi e 21. The gasoline vapors are distilled ofip in tower 9 and ass through pipe 15 to the condenser 23 an receiver 23 Steam may be assed into tower 9 throu h ipe 12. The a sorption oil substantial ree from absorbed constituents is passed t rough pipe 24 to heat exchanger 25 and cooler 25', and thence through pipes 26 and 5 back to the absorption tower 1.

In the exchanger 25 the hot stripped oil imparts some of its heat to the absorption stock. The preheated stock may then be passed through exchanger 27 to cool the hot product from tower 7. lIn this way the preheat of the absorption stock is increased to the desired value. Cooling of the liquid from the bottom of the tower 8 is ordinarily unnecessary.

By the use of series-connected towers as described, we are able to obtain a very satisfactory segregation of the desirable gasoline components. The butane product (which may contain some propane) from the tower 8 may be blended in 'suitable proportion with the'gasoline from tower 9, if desired. The gasoline from tower 9 may be sold as such but will ordinarily be blended with heavier gasoline. More or less of the butane product may be added to this blend or to the gasoline from tower 9.

The tower 7 is preferably operated under relatively high pressure, for example 15G-200 lbs.- per square inch. Even higher pressures,

up to 300 lbs. or more, may be utilized, especially when the temperature of the top of the tower is re ulated by means of cooling water and not y refrigeration. Avcooling liqpid will be supplied to the coil 1l in tower in such amount and at such a temperature as to cause the condensation of a substantial amount of the heaviest constituent that it is desired to remove from the tower, ordinarily propane. The reiuxing propane carries down with it heavier hydrocarbons that may be passing up the'tower.

The lower portion of the tower is adequately heated from the coil 12 so that iixed gases and most of the propane will be expelled from the absorption stock before it emerges from the tower through .pipe 19. The temperature in the lower portion of the tower 7 may vary between about 525,-625o F. and in the up er portion between about 20-40o F.

n the tower 8 the pressure is less, for eX- ample about 25-60 lbs. per square inch. The heating and cooling are similarly regulated to obtain an overhead product consisting mostly of butane, leaving the pentane and heavier gasoline hydrocarbons in the absorption stock. This tower may be so controlled asl to permit some butane to pass through wlth the absorption stock, since butane in limited amounts is desirable in the gasoline product. The temperature in the lower portion of the tower 8 may be about S50-450 F. and in the upper portion about 7 5-1'O0 F.

The tower 9 is utilized for the removal of the gasoline from the absorption stock. This may be done in any suitable wa It is desirable, however, to sup ly recti cation means similar to those descri ed in connection with towers 7 and 8, as in this way the possibility of carrying over some of the absorption oil is avoided. When using gas oil as the absorption stock, the lower portion of the tower 9 may -be heated to about BOO-350 F., the temperature in the upper portion being about 90-130D F. The pressure in tower 9 may be considerably lower than that in tower 8. Pressures from atmospheric to about 10 lbs, per square inch gauge ressure may be utilized in the tower 9. ubatmospheric pressures are not precluded here.

vIt will be understood that the various details of operation are subject to modification in accordance with the requirements of the gas being treated. Two rectification towers are a minimum requirement for our invention, but anydesired additional number of such towers may be used. In some cases the last tower ofthe series may be replaced by a steam still, or other means, for stripping out the gasoline from the absorption oil.

The segregation of the desired gasoline constituents by our rocess ma be designated absorptive rectification. t is characterized by the presence of the absorption liquid in the vapor-liquid contact zone, and is in this respect distinguished from prior processes in which rectification takes place in the presence of reflux formed only from the constituents being rectified. When cool, fresh absorption liquid is introduced into the upper portion of the rectifying towers, as described above, absorptive rectification takes place throughout the towers. Such absorption liquid may be used as a substitute for part or all of the cooling that would otherwise be necessary to prevent escape of desired components.

Various modiiications of procedure and apparatus may be made within the scope oi the appended claims, in which it is our intention to claim all novelty inherent in the invention, as broadly as the prior art permits.

We claim:

ll. Process of rectifying condensble constituents derived from a hydrocarbon gas, comprising passing relatively non-volatile absorption liquid charged with such constituents downward through a vapor and liquid contact zone, maintaining in such zone a pressure substantially above atmospheric,v heating the lower portion of the zone, and cooling the upper portion thereof to prevent desired components from escaping, whereby the condensible constituents are rectified in the presence of the absorption liquid, introducing-fresh, cool absorption oil into the upper portion of the Contact zone, withdrawlng the gases and vapors from the rectification to a point without the system, withdrawing the absorption liquid and subsequently separating the desired constituents therefrom.

2. Process of rectifying condensible constituents derived from a hydrocarbon gas and absorbed n a hydrocarbon oil miscible therewith and substantially. non-volatile at temperature and pressure ofthe rectification,

the improvement which comprises passing the charged absorption oil into the intermediate portion of a rectification zone maintained under a pressure materiallyabove atmospheric, positively cooling the upper portion of the rectication zone, taking oi from the upper portion of such zone the fixed gas content, including at least partl of the propane, of the absorption oil, passing the absorption oil from a lower portion of such zone into an intermediate portion of a second rectification zone maintained under a pressure above atmospheric but less than lthat in the first zone, positively cooling the upper portion of the second rectification zone, taking 0E from the upper portion of such second zone a substantial amount of the butane content of the absorption oil, taking ofi' from the lower portion of such second zone the absorption liquid substantially free from absorbed constituents other than gasoline constituents, then passin such absorption liquid into a zone in which t e gasoline constituents are expelled from the absorption oil, and recovering the gasoline constituents.

FRANK A. HOWARD.y 1 NATHANIEL E. LOOMIS. 

